Why the screen does not go out when talking on Xiaomi Redmi 9: a complete analysis of the problem

You put a Xiaomi Redmi 9 to your ear while you're calling, and the screen keeps glowing, and you accidentally push buttons, and the conversation turns into torture? This problem is familiar to many owners of Xiaomi budget smartphones, and it's not always related to breakdown. 80% of the time, the settings, the contamination of sensors or software failures that can be fixed on their own without going to the service center.

In this article, we’ll explore all the possible reasons why the Redmi 9 screen (including the Redmi 9A/9C/9T) doesn’t go out when you talk, from the banal disconnected proximity sensor to the board’s hardware malfunctions. You’ll get step-by-step instructions with illustrations, firmware tables, and answers to frequent questions. And if the problem turns out to be more difficult than you thought, you’ll learn how to diagnose the malfunction and how much it will cost to repair.

1. The proximity sensor: how it works and why it fails

The main reason why the Xiaomi Redmi 9 screen doesn't go out during a call is because the proximity sensor is not working properly, and this tiny sensor is located at the top of the screen (usually next to the front camera) and is responsible for turning off the backlight when you hold the phone to your ear, and if the sensor is contaminated, damaged or disabled programmatically, the system doesn't "understand" that you're talking, and the screen stays active.

How to check the proximity sensor on Redmi 9:

• 🔍 Visual inspection: Take a flashlight and shine it on the top of the screen, and the sensor looks like a small circular hole (sometimes closed with transparent film) if it's clogged with dust or covered with film/glass, that's the reason.
• 📱 Testing through the Engineering Menu: Enter the code ##6484## → Choose Proximity Sensor → If the values are unchanged (remain at 5.00 cm), the sensor is not working.
• 🛠️ Check in Safe Mode: Press the power button → Hold on to "Switch off» → If the sensor is running, it's the third-party app's fault.

On Redmi 9 (and other budget Xiaomi) often there is a defect of factory assembly: the sensor proximity is not glued to the screen tight enough, which eventually fades away, this manifests itself after falls or overheating the phone, in which case only reglazing the sensor in the service (cost – from 500 rubles).

2. Software failures: settings, firmware and application conflicts

If the proximity sensor is working, but the Redmi 9 screen is still not going out, the problem is the software part.

• 🔄 Reset sensor settings after update MIUI.
• 📲 Conflict with applications that intercept screen control (such as launchers or call recording programs).
• 🐞 Firmware bugs, especially in versions MIUI 12.5–13 for Redmi 9.

How to eliminate programmatic causes:

1. Turn on the sensor manually:
2. Reset your phone settings:
3. Update MIUI:

Make sure the sensor is not contaminated | Make a backup of contacts |Write down firmware versions and MIUI|Disable third-party launchers-->

If the problem occurs after you install a specific application (like Truecaller or Call Recorder), remove it and check the sensor.

⚠️ Attention: after resetting, you may lose access to your Xiaomi account if you don't remember your password!

3.Mechanical damage: what breaks down in Redmi 9

Xiaomi’s budget smartphones are not very durable, and the Redmi 9 is no exception. If the phone fell, wet or overheated, the reasons for the sensor’s failure may be hardware:

The most vulnerable spot in Redmi 9 is the proximity sensor plume that goes from the board to the top of the screen, which often detaches or rubs when it falls, and you can only check this by disassembling the phone or through the diagnostics in the service (free at official Xiaomi centers).

If the phone falls into water, don't try to dry it with a hair dryer or rice, it will aggravate corrosion, and it's better to take it to the service for cleaning with ultrasound.

4 Film, glass and cases: why they interfere with the sensor

One of the most common reasons why the Redmi 9 screen doesn't go out is because it's a closed proximity sensor, and many users glue full-screen protective glass or film without leaving any cutouts for the sensors, and even a thin film can block the infrared signal of the sensor, and it stops responding to the approach.

How to check:

• 📏 Take off the film/glass and check the sensor without them.
• 🔎 Light a flashlight through the glass – if the light does not pass through the sensor area, it is too dense.
• 📦 Check the case: some models with high sides cover the upper frame of the screen.

The solution is simple: use a glass with a cutout for the sensor or cut the film with scissors. Redmi 9 will fit glasses marked "Notch" or "For sensors." Examples of compatible models:

• 🛡️ Spigen Glas.tR EZ Fit (with a notch for sensors).
• 🛡️ Nillkin H+ Pro (precise fit for Redmi 9).
• 🛡️ Olixar Full Cover (only for models without sensor in the display).

💡

Before buying glass, check its compatibility with your Redmi 9 modification. For example, for Redmi 9T (NFC) and Redmi 9A (non-NFC) glass different because of the location of the sensors.

If you use a magnetically attached case (for example, for a holder in a car), the magnet can affect the sensor. Try calling without a case.

5. Custom firmware and root rights: risks and solutions

Redmi 9 owners who install custom firmware (like LineageOS or Pixel Experience) often encounter a failed proximity sensor.

• 🔧 No sensor drivers in unofficial builds.
• 🔄 A faulty kernel that does not support hardware functions.
• 🛠️ Conflicts with Magisk modules that change the system.

How to restore the sensor on custom firmware:

1. Check firmware compatibility with Redmi 9 (codenamed lancelot). For example, firmware for Redmi Note 9 (merlin) will not work.
2. Install the right core. MIUI-firmware will do lancelot_kernel, for AOSP — AOSP-lancelot.
3. Disable conflict modules in Magisk. Most often problems are caused by: Xposed Framework ViPER4Android (can block sensors) GravityBox

persist

TWRP

adb shell


rm -rf /data/property/persist.sys.proximity

If you are not sure of your actions, it is better to return the stock firmware through the Mi Flash Tool.

1. Download the latest official firmware for Redmi 9 (select Global Region).
2. Unpack the archive and launch MiFlash.exe.
3. Connect your phone in Fastboot mode (press Volume Down + Power).
4. Select the firmware folder and press Flash.

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Before repairing, make sure to back up the data! 90% of the time, when you repair hardware, the phone is reset to factory settings.

If the phone is warranty (up to 12 months from the date of purchase), contact the authorized service.

FAQ: Answers to Frequent Questions